Plants flourish best when they are supplied with water at a rate approximately equal to their use rate. Plant water use rates are known to vary widely, depending upon weather, plant size, plant type, soil makeup and location. Under watering tends to stress plants, while over watering can cause disease and other problems. Over watering also wastes valuable water resources and can cause excess leaching of fertilizers and pesticides to groundwater. Maintaining soil moisture conditions in the ideal range for individual plant vigor has been a long recognized need in irrigated agriculture and plant husbandry. This long felt need has heretofore gone unsatisfied.
Most current irrigation systems are either operated manually or are controlled by timers operating electric solenoid valves. In most cases the timer controlled systems are set to apply the same amounts of water on schedule regardless of the actual plant water requirements. The operation of manual irrigation systems is based on the visual observations of the operator and often does not correspond to soil moisture conditions either.
Most known prior art devices have attempted to measure soil moisture at a single or very small number of locations and supply a control signal to the main timer for a large irrigated area. No readily available device exists which accurately controls irrigation on a localized scale to plants and which can be used with commercial irrigation distribution components.
The following patents reflect the state of the art of which applicant is aware, insofar as these appear germane to the patent process. These patents are disclosed with a view towards discharging applicant's acknowledged duty to disclose relevant prior art. However, it is respectfully submited that none of these patents teaches the claimed invention when considered singly, and none of the patents renders obvious the instant invention when considered in any conceivable combination.
______________________________________ INVENTOR PATENT NO. ISSUE DATE ______________________________________ RICHARDS 2,445,717 July 20, 1948 RICHARDS 2,674,490 April 6, 1954 RICHARDS 2,863,698 Dec, 9, 1958 TREIRAT 3,747,399 July 24, 1963 CRANE 3,758,987 Sept. 18, 1973 HUNTER 3,981,446 Sept. 21, 1976 LOHOFF 4,055,200 Oct. 25, 1977 HUNTER 4,274,583 June 23, 1981 ______________________________________
Tensiometer type devices, such as that found in Richards, have had the disadvantage of requiring regular maintenance for proper operation. Other devices of interest have sensed the bubbling pressure of a controlled porosity block or sensor and in turn actuated a valve or controller. Some of these devices (e.g., Hunter) require a significant elevation differential to operate and therefore must protrude high up out of the ground, leaving them in the way of cultural practices. Others (e.g., Crane and Treirat) have very special water supply or water distribution equipment requirements. The patent to Lohoff appears to be of particular interest as it uses line water pressure for operation, but relies on a complex interaction of a solenoid, multiple chambers, and contacts as a pilot for a main water control valve.
Almost all of the devices described above have the disadvantage of scheduling irrigation for a large number of plants in a wide area based on moisture measurement at a single spot. In most landscaping applications and many agricultural applications this approach can be substantially inaccurate in supplying individual plants with the proper amounts of water. Moisture regulating irrigation devices shown in prior art for use with individual plants or small groups of plants are designed with a gravity water supply tank or require ultrafiltration. These are very cumbersome for outdoor landscaping and agricultural applications.
In contrast, the instant invention is directed to a soil moisture sensitive irrigation control device which allows irrigation water to be distributed in conjunction with commercially available equipment to accurately fulfill the requirements of individual plants or small groups of plants.